We have used chromosome 18-specific painting probes to analyze early stages of oogenesis in two human trisomy 18 fetuses. At leptotene, a diffuse, nonlinear chromosomal fluorescence was detected as one (27), two (42), or three (31 ) signals in 534 cells. The variation in size of these signals implies the possibility of associations between homologs prior to zygotene. At pachytene, about 75 (339/453) of the cells had a trivalent configuration, and almost half of these cells exhibited almost complete triple synapses. Approximately 24 of the pachytene cells demonstrated a bivalent:univalent configuration, and 1 exhibited complete asynapsis. Our data imply that triple synapses may be a regular feature of meiosis involving multivalents.
展开▼
